Summary for spot passivation Discussion
Spot passivation for an assembled, laser-welded 17-4 part with a plastic component is usually done by applying a brush-on paste or thickened acid, or spraying a liquid, rather than submerging the whole part. In the reply, Justin Steccato is told that the treatment should sit for the time required by the applicable standard for a room-temperature process, then be rinsed thoroughly and dried. Testing can still follow the standard being used, but the part size may limit options; the answer notes that copper sulfate is generally acceptable, and ASTM A967’s wet cloth test is the fallback. The responder also asks who is restricting citric passivation approval, suggesting the customer may be the limiting factor. No special neutralization step is mentioned in the reply, and the practical emphasis is on careful local application, complete rinsing, and choosing a test method that fits a spot-treated assembly.
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Q. Hello all,
I am required by my customer to perform spot passivation on a Laser welded assembled part made out of 17-4 and a plastic component. I have not performed spot passivation before and was looking for some advice. We have a Nitric 2 Passivation line currently, and are not approved for citric.
Does anyone have any advice on how to make this go smoothly? Any recommendations on what swabs to use, and how to test the parts after? Or what to look out for?
I’m concerned on how to test the parts as all of the test methods we currently use involve submerging or spraying the entire part.
Additionally, do i just walk the part down our normal clean line, but instead use a swab at every step instead of submerging the part? Or is general practice just to clean off the weld, swap passivation, and then clean again? Is there any need for neutralization?
Justin Steccato
– New Jersey
April 4, 2025
Justin,
The typical procedure for spot passivation is to brush on a paste/thickened acid (or spray it on for a liquid), let it soak the amount of time called for by the standards for a room temperature treatment (i.e. at least 20 minutes for citric per ASTM A967), then rinse the acid off thoroughly and let it dry.
Testing can be per any of the methods provided for in the standard being used, though of course that’s limited by the size of the item. Copper sulfate is generally fine, A967’s wet cloth test would be the fallback from there.
When you say you are not approved for citric, that would be not approved by whom? The customer?
(Adv.) If you are in need of citric acid passivation products for this, my company can assist.
Ray Kremer
Stellar Solutions, Inc.
McHenry, Illinois
